<button (click)="showBlock = !showBlock">toggle visible</button>
<div class="jumbotron" *ngIf="showBlock else elseBlock">
  <h1 class="display-4">Hello, world!</h1>
  <p class="lead">This is a simple hero unit, a simple jumbotron-style component for calling extra attention to
    featured content or information.</p>
  <hr class="my-4">
  <p>It uses utility classes for typography and spacing to space content out within the larger container.</p>
  <a class="btn btn-primary btn-lg" href="#" role="button">Learn more</a>
</div>
<ng-template #elseBlock>
  <p>showBlock为假时显示</p>
</ng-template>